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34

PRACTICAL  ORGANIC  CHEMISTRY

furnished with a side tube, for introducing the substance, but it is
not necessary. It is provided with a stirrer. A Beckmann
thermometer completes the apparatus. This is fixed through a

cork so that the bulb
nearly touches the bottom
of the tube, a wide slit
being cut in the side of
the cork for moving" the
stirrer. The Beckmann
thermometer is of special
construction and requires
explanation. As the
method involves merely
an accurate determination
of small differences of
temperature, it is not re-
quisite to know the exact
position on the thermo-
meter scale. The Beck-
mann thermometer regis-
ters 6 degrees, which are
divided into hundreclths.
The little glass reservoir
at the top (a, Fig. 30)
serves the purpose of
adjusting the mercury
column to different parts
of the thermometer scale
by adding or removing
mercury from the bulb.

Freezing-point De-
termination.  In  the
example to be described,
IMG. 3o.                          pure benzene (see p. 136)

is  used   as   the  solvent

Carefully dry the inner tube. Fit it with a cork and weigh it
together with the cork suspended by a wire to the arm of the
balance. Introduce sufficient benzene to cover the bulb of the
Beckmann thermometer when it is pushed nearly to the bottom
of the tube. About 10 c.c. will be found to be sufficient Insert